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Smelting Furnace Dust Recovered.--The International Nickel Company of Canada, Limited, like the ordinary housewife, has its dust problems, but with a difference. The Inco dust is a special variety containing-small quantitities of nickel and copper and is produced in operations of the Company's huge smelter here. This dust is recovered at a daily rate of hundreds of tons and turned back into production instead of being allowed to escape into the air.
Recovery of the dust contributes to plant efficiency by making otherwise waste material available for production. The dust is recovered from gases from the batteries of roasters and converters in the smelter--which is the largest of its kind in the world--and is used again in the nickel reverberatories. This giant dry-cleaning operation is carried on in the Cottrell precipitation plant, which operates at such high efficiency that only a small percentage of furnace dust gets by.
On their way to the plant's 500-ft. smoke stack the gases pass into huge flues in the treater section of the Cottrell plant in which are suspended twistedwire curtains charged with 60,000 volts of electricity. Parallel to the wire curtains are grounded 22-ft. rods which act as collecting electrodes. Receiving this big electric shock, the ionized particles of dust are precipitated on the rods and the gases pass on to the stack. Once during each shift the power is turned off in each unit 'of the treater section and the rods are tapped by pneumatic hammers to knock off the dust, which falls into bins. Picked up by a conveyor, the dust is transported to a shooting tank which blows it through pipes to the reverberatory furnaces where it re-enters the smelting process.
Power for the CottreU operation is received at 550 volts a.c. and in a battery of transformers and rectifiers is stepped up to 60,000 volts d.c. On either side of each rectifier are coils which prevent interference with radio reception in the area. All openings giving access to high-tension equipment or electrodes are protected by automatic grounding switches to prevent workers from coming into accidental contact with live parts carrying high voltage.
The temperature of the gases as they pass through the treater section is watched constantly. If it falls below a certain point the result is a condensation of acid which corrodes the equipment. Heat from the reverberatory furnace boilers is used to overcome this difficulty. Continuous Vacuum Melting Furnaces.--U. S. Patent No. 2,625,719 has recently been granted to the National Research Corporation of Cambridge, Massachusetts. The patent covers continuous vacuum melting furnaces which have been developed by the Metallurgical Department.
This new development now makes it possible to charge raw material and remove vacuum cast ingots from furnaces without the necessity of cooling the crucible or breaking the vacuum in the melting chamber. Vacuum melting furnaces are used in the production of titanium, zirconium, and molybdenum and in the production of specialty metals and alloys used where the ultimates in physical, chemical, and electrical properties are required.
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